Kinetics for Reversible Menschutkin Reactions. The Effects of Variations in Reactant Structures on the Sensitivity of the Reaction Rate to Solvent Variations

The reaction rates and equilibrium constants for quaternization of N,N-dimethylaniline and its derivatives with methyl iodide have been measured in acetonitrile, acetone, tetrahydrofuran, nitrobenzene, benzene, benzyl alcohol, and methanol at various temperatures. There is an approximate tendency for the solvent dependence of the reaction rates to diminish linearly with increasing reactivity of nucleophile. This could be interpreted in terms of the theory of an absolute reaction rate and of the concept of the rise of interaction term. In this connection it was proposed that such a problem must be considered in terms of the unitary term of rates. Using the data of rates of the reaction between pyridine and methyl iodide in various solvents, the activity coefficients of dimethylaniline and its derivatives in methanol relative to that of pyridine are estimated. Some inferences have been drawn concerning the nature of SN2 transition state from effects of solvents on both rates and equilibria.